The Contemporary System

The depth, breadth, and complexity of the global ocean, covering more than 70 percent of Earth's surface, have challenged our ability to explore, measure, and comprehend its controlling processes and to predict its behavior. Technology has evolved to the point where we can study the ocean on a global scale and study its interactions with the land and the atmosphere. Such studies have gained increased importance because expanding populations and development, and an increase in atmospheric carbon dioxide and other greenhouse gases, will impact the physical, chemical, biological, and geological processes in the global ocean. Interactions among these processes are responsible for the distribution and abundance of plants and animals in the ocean and also produce our climate.

Changes in climate are a critical factor governing life on Earth, and the ocean plays a significant role in climate control. An understanding of short-term, coupled atmosphere-ocean effects like the El Niño-Southern Oscillation (ENSO) can have immediate economic and societal impacts. Agricultural production, and therefore food supplies and economies, is directly affected by climate variations. Changes in climate and the response of the ocean will greatly affect coastal areas resulting in rising or falling sea-level, changes in coastal upwelling, and seawater intrusion into freshwater aquifers. We must understand the role of the ocean and sea ice in climate change, particularly changes in atmospheric gases like carbon dioxide, in order to make predictions and minimize adverse effects on humankind.

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"THE CONTEMPORARY SYSTEM."
The Ocean's Role in Global Change: Progress of Major Research Programs.
Washington, DC: The National Academies Press, 1994.

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The Ocean's Role in Global Change: Progress of Major Research Programs
The Contemporary System
The depth, breadth, and complexity of the global ocean, covering more than 70 percent of Earth's surface, have challenged our ability to explore, measure, and comprehend its controlling processes and to predict its behavior. Technology has evolved to the point where we can study the ocean on a global scale and study its interactions with the land and the atmosphere. Such studies have gained increased importance because expanding populations and development, and an increase in atmospheric carbon dioxide and other greenhouse gases, will impact the physical, chemical, biological, and geological processes in the global ocean. Interactions among these processes are responsible for the distribution and abundance of plants and animals in the ocean and also produce our climate.
Changes in climate are a critical factor governing life on Earth, and the ocean plays a significant role in climate control. An understanding of short-term, coupled atmosphere-ocean effects like the El Niño-Southern Oscillation (ENSO) can have immediate economic and societal impacts. Agricultural production, and therefore food supplies and economies, is directly affected by climate variations. Changes in climate and the response of the ocean will greatly affect coastal areas resulting in rising or falling sea-level, changes in coastal upwelling, and seawater intrusion into freshwater aquifers. We must understand the role of the ocean and sea ice in climate change, particularly changes in atmospheric gases like carbon dioxide, in order to make predictions and minimize adverse effects on humankind.

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The ocean and the atmosphere store heat derived from solar radiation and redistribute the heat from equatorial to polar regions. The thermal inertia of the ocean may reduce the speed of transition from one climate regime to another, as the slow overturning of the deep-ocean limits heat absorption and release at the ocean surface. The ocean is also a major source and sink for gases and chemicals that effect climate, such as carbon dioxide, water vapor, and dimethyl sulfide. Evaporation from the ocean is the main source of water for the global hydrological cycle, in which moisture is distributed by atmospheric motions and returned through precipitation, either directly to the ocean or indirectly as runoff from the continents. The deep circulation of the ocean is strongly coupled to surface processes in polar regions. Most water that flows to the ocean bottom is formed in these regions as surface water becomes colder (through interaction with cold overlying air) and saltier (through ice formation). The sinking of this dense water can have a large effect on global climate because it carries greenhouse gases and heat with it to the ocean bottom, out of contact with the atmosphere for hundreds of years. Formation of deep water in the North Atlantic Ocean can be diminished and reestablished over decadal time scales. There is increasing evidence that anomalously hot summers or cold winters in the United States are related to particular ocean conditions that cause distortions in weather patterns across the country for weeks at a time.
At certain times, developments in basic understanding and technology coalesce to produce dramatic advances. Such a breakthrough is now possible in ocean science with new observational tools and techniques, such as remotely operated vehicles, satellite-borne sensors, trace chemical measurement, acoustic techniques, long-life buoys and floats, and seafloor seismometers. Progress in electronics has provided supercomputers and work stations that can facilitate the processing and analysis of data and the construction of detailed models. The new technology and innovative ideas now available have provided the basis for developing scientific programs on a scale that has not been attainable previously. Successful initiation and completion of the inter-disciplinary global experiments described in this report could produce a tremendous increase in our understanding of how Earth works as a system.
The World Climate Research Program (WCRP) began in the early 1980s, using new in situ and satellite measurement techniques. It is aimed at understanding long-term weather variability and climate change. In recognition of the central role of the ocean in these processes, WCRP has focused on understanding the interaction of the ocean and the atmosphere. Programs falling

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under the aegis of WCRP include the Tropical Ocean-Global Atmosphere (TOGA) program and the World Ocean Circulation Experiment (WOCE). In addition, WCRP will continue to study the processes that control the exchange and transport of energy and water within the global climate system. These programs, for which the United States is providing considerable resources, furnish a context for much of U.S. ocean science research.
The International Geosphere-Biosphere Program (IGBP) is aimed at describing and understanding the interactive physical, chemical, and biological processes that regulate the total Earth system, the unique environment it provides for life, the changes that are occurring in that system, and the manner in which these changes are influenced by human actions. The Joint Global Ocean Flux Study (JGOFS), Marine Aspects of Earth System History (MESH), and Land-Ocean Interactions in the Coastal Zone (LOICZ) programs, which are described in this report, are elements within the IGBP. [The Past Global Climate (PAGES) program is also an IGBP element, though it is not included here.]
Global Ocean Observing System
The Global Ocean Observing System (GOOS) program will initially emphasize those observations needed for prediction of the El Niño-Southern Oscillation (ENSO), the consequent rainfall and temperature patterns, and observations needed for detection of global change due to greenhouse warming, such as absolute sea-level and average ocean temperatures. GOOS is planned to have five application modules, including climate, living marine resources, marine weather and operational ocean services, health of the ocean, and the coastal zone. The climate module of GOOS provides the oceanic component of the Global Climate Observing System (GCOS) and includes the efforts related to global long-term climate change. GOOS will be based in so far as possible on operational measurements (i.e., observations made routinely, essentially permanently, and with societal needs in mind). GOOS is led by the Intergovernmental Oceanographic Commission (IOC) in cooperation with the World Meteorological Organization (WMO), the International Council of Scientific Unions (ICSU), and the United Nations Environment Program (UNEP).

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Drawing strongly upon the successes of the TOGA program, the main observational systems for GOOS will initially be moored buoys, primarily in the tropical Pacific; volunteer observing ships; drifting buoys; island tide gauges; and satellites to measure sea-surface temperature and determine surface topography. Future instrument systems might include autonomous profilers [e.g., Autonomous Lagrangian Circulation Explorer (ALACE)], acoustic sensing of average ocean temperature, and in situ biogeochemical measurements. Overlaid on the measurement systems will be satellite telemetry, quality control, and data management, all of which exist now but need improvement and expansion. The design and enhancements of GOOS are based on the current research programs described in this report, planned future programs, and close cooperation between the research and operational communities. Several of the programs described in this report will also furnish important contributions to the development and operation of GOOS.
Tropical Ocean-Global Atmosphere Program
The Tropical Ocean-Global Atmosphere (TOGA) program was designed as the first major World Climate Research Program (WCRP) project and concentrates on the study of the ENSO cycle. The Southern Oscillation is a seesaw-like variation, over several-year intervals, of barometric pressure differences between the South Pacific Ocean and the western Pacific/eastern Indian Ocean. El Niño is a manifestation of the warm phase of the cycle, in which the pool of warm water normally observed in the western Pacific Ocean shifts eastward, diminishing upwelling of cold water along the coast of western South America and along the equator and shifting rainfall patterns away from Australia and Indonesia and eastward into the Pacific. The economic impacts of excess rainfall and flooding in South America and droughts in Australia alone are estimated to be in the billions of dollars.
The U.S. TOGA program has been concerned primarily with studies of the ENSO cycle in the tropical Pacific Ocean and its effect on global climate. The observational phase of TOGA started in 1985 and runs through the end of 1994.
The TOGA program was designed to (1) describe the interactions between the tropical oceans and the global atmosphere in sufficient detail to determine the predictability of the global climate system on seasonal to interannual time scales, (2) understand how and why these ocean-atmosphere interactions occur,

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(3) model the coupled system for the purpose of predicting its variations, and (4) design a data collection and distribution system sufficient to achieve the first three objectives. The program includes process studies, long-term observations (over several ENSO cycles), and modeling. Modeling efforts aim to provide a quantitative description of ocean and atmosphere characteristics and to explain why and how these characteristics change over time and space. Coupled TOGA models, used for both simulation and prediction, require data on windstress (which drives surface ocean currents) and sea-surface temperature, in addition to the thermal structure of the upper tropical Pacific.
At present, data are collected regularly from the TOGA Observing System consisting of: (1) the TOGA Tropical Atmosphere Ocean (TAO) array—approximately 65 moored buoys that incorporate instruments to measure the surface winds and the thermal structure of the upper ocean and telemeter the information instantaneously to satellites for immediate distribution through the Global Telecommunications System (GTS), where it is used for research and weather prediction; (2) a network of several equatorial moorings that measure the vertical structure of currents; (3) the TOGA sea-level network—sea-level gauges in the Pacific and Indian Ocean; (4) a Voluntary Observing Ship (VOS) network that measures upper ocean temperature from expendable instruments dropped from merchant vessels in all three tropical oceans; (5) a drifting buoy array that measures tropical sea-surface temperatures and near surface currents; (6) a drifting buoy array that measures sea-surface temperature and sea-level pressure over all three tropical southern oceans; and (7) a Trans Pacific Profiler Network consisting of eight radar sites that measure atmospheric wind profiles.
The TOGA Coupled Ocean-Atmosphere Response Experiment (TOGA COARE), a major process experiment in the eastern Pacific, has just been completed (Box 2). This experiment measured processes influencing interactions between the atmosphere and the warm-water pool in the western Pacific Ocean, including measuring the convective processes in both the atmosphere and ocean that influence these interactions.
The TOGA Program on Seasonal to Interannual Prediction (T-POP), a research program, has been instituted to develop the models and methods needed to provide socially useful predictions of aspects of ENSO a month to a year in advance using data provided by the TOGA Observing System (Box 2). Program participants include scientists from the National Atmospheric and Oceanic Administration (NOAA) and National Aeronautics and Space Administration

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(NASA) laboratories, the National Center for Atmospheric Research, and several U.S. universities working on coupled dynamic models for prediction. Informal participation by international colleagues is encouraged.
Planning is under way to form a multinational center, the International Research Institute for Climate Prediction (IRICP), with the following goals: (1) to institutionalize and regionalize short-term climate predictions for the benefit of those nations affected by ENSO variations and (2) to train people from those countries to make, understand, and use these predictions for social and economic benefit. The operating concepts embodied in the IRICP are being demonstrated in a pilot project currently in operation at Lamont-Doherty Earth Observatory.
Because the observational phase of TOGA is drawing to a close, a planning process has been under way both nationally and internationally for programs to maintain and expand the TOGA Observing System as appropriate and to use and expand the prediction results of TOGA. Internationally, the World Climate Research Program is planning the Climate Variability and Predictability (CLIVAR) program whose designated Focus 1 will be on seasonal to interannual global variations and predictability. Nationally, the United States is planning the Global Ocean-Atmosphere-Land System (GOALS) program, a contribution to CLIVAR Focus 1. Efforts are also under way to transfer parts or all of the TOGA Observing System, developed initially as a research observing system, to a permanent observing system in support of the Global Ocean Observing System for use in regular and systematic prediction.
The U.S. component of TOGA is a coordinated effort among NOAA, NASA, the National Science Foundation (NSF), and the Office of Naval Research (ONR). Nationally, the TOGA program was managed by the U.S. TOGA Office which coordinated interagency funding and was advised by the NRC/TOGA Advisory Panel. Internationally, the program was managed by the International TOGA Office, funded by the Intergovernmental TOGA Board, and advised by the TOGA Scientific Steering Group.

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Box 2—Major TOGA Accomplishments
Creation and maintenance of the TOGA Observing System, consisting of XBTs (Expendable Bathythermographs), drifters, the TOGA TAO array, a current meter array, a sea-level network, and a set of atmospheric sounding radars.
Measurement of the thermal state of the upper ocean and the winds over several ENSO cycles from 1985 to 1995, including the warm phases of 1986–87, 1991–92–93, and the cold phase of 1987–88.
Development of climatologies of sea-surface temperature (SST), currents, subsurface thermal structure, and surface winds through measurements by the TOGA Observing system.
Development of an operational SST product involving satellite observations combined with in situ drifter measurements.
Development of an operational ocean model for assimilating Pacific Ocean observations and creation of gridded data fields for the entire tropical Pacific for use in research and prediction.
Creation of a set of data centers for the quality control, archiving, and dissemination of TOGA data, in particular the Subsurface Data Center in Brest, France; the Upper Air Data Center in Poona, India; and the Sea-Level Center in Hawaii.
Development of coupled atmosphere-ocean models for the simulation of ENSO and subsequently development of theoretical ideas about the genesis and evolution of ENSO, in particular the ''retarded oscillator mechanism.''
Design and conduct of several smaller process studies (Tropic Heat Experiment, Tropical Instability Wave Experiment, Equatorial Mesoscale Experiment) and a major international process experiment (TOGA COARE) involving aspects of ENSO in and over the tropical Pacific.

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Demonstration of the ability to predict aspects of ENSO a year or so in advance and establishment of routine and systematic predictions, thereby opening the new age of short-term climate prediction.
Set up the TOGA Program on Seasonal to Interannual Prediction (T-POP) to develop the coupled dynamical models and other elements necessary for the regular and systematic prediction of climate a year or so in advance, initialized with the data provided by the TOGA Observing System.
Fostering a program to reanalyze of the global atmospheric data, thus creating a climate data set so that TOGA coupled models would have an initialization and validation set for climate prediction.
Participation in the design of the International Institute for Climate Prediction, a major multinational institute for predicting aspects of ENSO a year or so in advance and for maximizing the social and economic utility of these forecasts by forging partnerships with countries most in need of these forecasts.
Summary
The original aims of the TOGA program were to investigate the feasibility of predicting interannual variations in the tropics characteristic of ENSO, to design an observing system to understand the ENSO phenomenon, and to initialize predictions of ENSO. A TOGA Observing System has been established in the tropical Pacific to relay surface and subsurface information to the GTS in real-time. Data collected with the TOGA Observing System has helped develop coupled atmosphere-ocean models for the simulation of ENSO events. Using these models and data collected continuously by the TOGA Observing System, researchers have demonstrated that there is significant skill in predicting some aspects of ENSO a year or so in advance (the prediction is a noticable improvement over a prediction that relies solely on the seasonal cycle). The first real-time ENSO forecast using coupled models was made in early 1986, and this ability has since been demonstrated by a number of coupled prediction systems. Today, experimental ENSO forecasts are published routinely.

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As a result of TOGA, scientists are now close to establishing a regular and systematic climate prediction capability, using coupled models and sophisticated data assimilation systems, and an operational observing network to support this capability. Accomplishments in these areas have been substantial (Box 2). Predictions have been used advantageously by numerous countries, including the United States, Peru, Brazil, and Australia, for agricultural and water resources planning. Although few studies of the economic impact of ENSO events have been carried out, it has been estimated that the ability to predict an El Niño event at least 6 months in advance with a 60 percent probability, could save the U.S. agricultural sector alone between $0.5 and 1.1 billion per event—the average annual savings would be $183 million per year over a 12-year period (Workshop on the Economic Impact of ENSO Forecasts on the American, Australian, and Asian Continents, 1993). Assuming that forecasts continue to become more skillful, the ability to anticipate climate and mitigate its effects in the United States and other nations could result in even larger savings in the agricultural, fisheries, and water resources sectors of the economies.
World Ocean Circulation Experiment
Ocean circulation is related to climate on a decades-to-centuries scale, through the transfer of heat, momentum, and greenhouse gases between the atmosphere and the ocean. Thus, in order to understand and predict global climate change, on these time scales improved understanding of ocean circulation is crucial. To that end, the WCRP established the World Ocean Circulation Experiment (WOCE).
WOCE studies surface and subsurface circulation of the global ocean. The field program began in 1990 and extends through 1997; it is anticipated that the synthesis phase will continue until 2005. The primary WOCE goal is to understand ocean circulation well enough to model its present state, to predict its future state under a variety of assumptions, and to predict feedback between climate change and ocean circulation. This goal will be met by describing (1) present ocean circulation and variability, (2) air-sea boundary layer processes, (3) the role of exchange among different ocean basins in global circulation, and (4) the effect of oceanic heat storage and transport on the global heat balance.
The WOCE program consists of several related parts, the largest of which is a global survey called Core Project 1 (Box 3). This cooperative international

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project integrates measurements from satellites, voluntary observing ships (VOSs), moorings, subsurface floats, surface drifters, tide gauges, and research vessels. This global hydrographic survey measures (1) water density; (2) various natural tracers, such as salinity, oxygen and nutrients; and (3) man-made tracers of water motions, such as chlorofluorocarbons (CFCs). Subsurface floats and current meter moorings augment the global survey with direct observations of ocean current velocity. Objectives of the survey are to (1) quantify oceanic transport of heat and the pathways of downward water movement by which atmospheric gases are transported into the deep ocean and (2) provide data to model observed circulation patterns. An upper ocean program will focus on the atmosphere-ocean fluxes that drive the ocean, feedback to the atmosphere, and variations in upper ocean temperature and heat storage.
The U.S. contribution to Core Project 1 began in 1991 in the Pacific Ocean and will be completed by mid-1994. Unfortunately, there will likely be a large gap in coverage in the western North Pacific, where commitments of other nations will not be met. Following the Pacific, U.S. attention will turn to the Indian Ocean, where a major international effort is planned to begin in late 1994 and continue into 1996. U.S. Core Project 1 work in the Atlantic, other than expendable bathythermograph deployments that began in 1990, is still undecided but is scheduled to begin in 1996.
Work in the Southern Ocean (Core Project 2) concentrates on the Antarctic Circumpolar Current (ACC), which connects the Atlantic, Pacific, and Indian oceans, and its interaction with the waters to the north and south. This program includes studies of the formation and spread of cold, dense, high-latitude water masses, as well as measurement of surface temperature, pressure, and velocity from surface drifters. Time series and repeat hydrographic measurements in the areas south of America, Africa, and Australia, together with altimetric measurements from satellites, will give insight into the variability of the ACC. Unfortunately, at present there is little chance of long-term absolute measurements of the transports because of the expense associated with setting up large enough mooring arrays.
Core Project 3 focuses on specific processes important to ocean circulation and modeling. The Subduction Experiment (1991–93) examined the process by which surface water is conditioned and mixed downward into the thermocline. The Tracer Release Experiment (1992–93) has provided the first direct open ocean measurements of vertical and lateral diffusivity of a tracer (the inert,

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anthropogenic substance, sulfur hexafluoride). The Deep Basin Experiment is examining deep and abyssal flow in the Brazil Basin. These three process studies have been carried out principally by U.S. scientists with assistance from scientists from the United Kingdom, Germany, and France. Enhanced sampling of the North Atlantic Ocean (especially with repeat hydrography, floats, and drifters) is planned through international cooperation and joint work with the Atlantic Climate Change Program (ACCP). However, the full suite of planned Core Project 3 studies is not likely to be implemented because of budgetary constraints.
Progress toward WOCE objectives has resulted in part from a series of technological improvements including: (1) improved meteorological observations from ships and buoys, (2) a new accelerator mass spectrometry facility for measuring radioactive carbon (14C), (3) improved methods for extracting and measuring CFC and helium/tritium, (4) a new type of acoustic Doppler current profiler, (5) autonomous pop-up floats that report their position via Argos satellites at intervals of several weeks for periods up to 5 years, (6) better surface drifters fitted with surface pressure sensors, and (7) an automatic XBT launcher. New procedures for quality control and storage of data have been developed. These will ensure that the WOCE data set remains internally coherent and will be of use for many years in the future.
Despite setbacks, there has been considerable progress toward a better description of general ocean circulation and improvements in modeling ocean circulation. The incorporation of CFC, helium/tritium, and 14C sampling into the hydrographic program is providing a global ocean inventory of these tracers for the first time—an important environmental baseline for the global change research community. Also, the first heat transport analyses addressing the role of the global ocean are being completed currently and will be refined as WOCE proceeds. There has also been steady progress toward improved surface specification of boundary conditions and model-based estimates of surface flux. Major advances have been made in our ability to establish a truly global model of the ocean, with realistic time and space scales. U.S. support for the program comes from NSF, NOAA, ONR, NASA, and the Department of Energy (DOE).

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Summary
The goal of the U.S. GLOBEC program is to conduct scientific investigation into the linkages among climate, ocean physics, and marine animal populations. If these linkages are understood, then the responses of marine ecosystems to potential future climate changes, whether anthropologically induced or natural, can be predicted, assessed, and better managed. In addition, GLOBEC supports the development of new technologies (i.e., acoustic, optic, and molecular) that promise higher resolution or more cost effective ways to measure the structure and condition of ocean ecosystems and the status of living marine resources.
The first GLOBEC field programs have just begun and accomplishments to date are preliminary (Box 6). A pilot study of the role of water column stratification on the feeding and behavior of larval cod and haddock on Georges Bank suggests that vertical migratory behavior plays an important role in retaining the larval stages of these commercially important species in favorable environments for growth, survival, and recruitment. Eventually, U.S. GLOBEC research on groundfish species (cod, haddock) on Georges Bank may provide the scientific underpinnings for a rational rebuilding of these historically important commercial stocks and of the fishing industry that is dependent upon them.
Finally, U.S. GLOBEC emphasizes the development of coupled physical and biological diagnostic models to understand existing conditions, with the goal of then using them as prognostic tools to assess potential conditions and responses in the future. These prognostic tools will permit better management of marine ecosystems providing stability, profit, and sustainability.
Atlantic Climate Change Program
The Atlantic Climate Change Program (ACCP) is aimed at understanding large-scale air-sea interaction between the Atlantic Ocean and the global atmosphere. Much of the early emphasis of ACCP is directed at middle and high latitudes of the North Atlantic for several reasons. First, the subarctic North Atlantic is the only site in the northern hemisphere where convection in the ocean extends from the surface to deeper levels, providing a mechanism for creating persistent sea-surface temperature anomalies one decade to century time scales. Second, there is a good correlation between sea-surface temperature in

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the northwestern Atlantic and atmospheric surface temperatures averaged over the entire northern hemisphere. For example, the "dust bowl" in the western United States in the 1930s was accompanied by pronounced warmth over the northern North Atlantic. Similarly, the relatively cool climate of the late 1960s and early 1970s was associated with very low sea-surface temperature in the western Subarctic North Atlantic. Finally, in the context of assessing global climate change due to anthropogenic causes, understanding the very low frequency, apparently natural variability 'of climate will help answer the question: Can we discriminate natural climate variability of very long time scale from the possible effects of human-induced greenhouse warming?
To study these phenomena, ACCP has adopted a three-pronged approach—analysis of historical data, modeling, and direct observation and monitoring of the ocean. The first step in ACCP has been to assemble and examine Atlantic Ocean data collected in the past. The second element of the program is an attempt to validate a whole hierarchy of atmospheric and ocean models using these data. The model hierarchy is intended to range from simple conceptual models to numerical models that link the global ocean and atmosphere. These models are aimed to better understand high-latitude air-sea interactions and to help design an effective system for monitoring low-frequency changes in water mass properties and in the heat balance, which may be linked to persistent sea-surface temperature anomalies. The final element of the program will be to test and deploy instruments for monitoring winds, seasurface temperature, sea ice, and water mass properties and to combine that information with other measurements from satellites, drifting instruments, and ships of opportunity. ACCP will coordinate closely with WOCE in North Atlantic studies.
ACCP analysis of historical data has indicated two types of low-frequency climate variability over the North Atlantic. One type has a period of about a decade with marked observational signatures in surface winds, sea-ice coverage, and sea-surface temperature. A second type has a period of four to six decades and appears to be associated with polar-amplified climate variations affecting the entire northern hemisphere. Its observational signature is in the ocean temperature and salinity fields, both at the surface and at depth. The accompanying atmospheric anomalies are weaker than those of the decadal mode and show a markedly different structure. Why this difference should exist between the decadal and the multidecadal time-scale climate fluctuations is an open question being investigated by ACCP modelers.

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An abrupt change in the climate regime of the Atlantic Ocean occurred in the late 1960s and early 1970s. This was associated with the formation of a very large patch of low salinity water in the northwest Atlantic, which has been dubbed "The Great Salinity Anomaly." This anomaly drifted off to the east after a few years, but while it was in the Labrador Sea it apparently caused a major disruption of normal wintertime convection in the ocean, leaving a clear signal in surface, as well as deepwater mass properties. Though historical record is incomplete, there is evidence to indicate that a similar event may have taken place around 1910 in the Labrador Sea. It is not clear whether these extreme surface salinity events are associated with the decadal or multidecadal climate variations.
Some of the most important accomplishments of the ACCP have been in the area of modeling. Atmospheric models have shown that the response to high-latitude sea-surface temperature anomalies is much more complicated than, and fundamentally different from, the response to tropical sea-surface anomalies. The chaotic nature of middle and high latitude flows prevent any simple, linear response patterns from emerging, in which cause and effect could easily be identified. This insight explains the confusing results obtained in previous studies of atmospheric response to high-latitude sea-surface temperature patterns.
Ocean models with boundary conditions which mimic the effects of air-sea interaction provide the simplest illustration of how changes in the ocean's thermohaline circulation and in high-latitude ocean convection provide an explanation for low-frequency climate variability in the North Atlantic. Rapid progress has been made in clarifying the early results obtained with these models, which showed that two very different solutions could exist for the same boundary conditions. These results show how the different salinity patterns that may have existed during the last Ice Age could lead to a very different, and greatly amplified, type of climate variability than has existed over the past few thousand years.
Perhaps the single most important accomplishment in modeling has been the simulation of multidecadal Atlantic climate variability by the Geophysical Fluid Dynamics Laboratory (GFDL) global coupled ocean-atmosphere model (Box 7). In 1,000-year-long integration, multidecadal variability associated with changes in strength of the thermohaline circulation comes out clearly. The sea-surface temperature anomalies produced by the model also match the decadal time-scale anomalies observed in the North Atlantic. This successful simulation provides

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an important building block for future ACCP modeling studies and for the design of practical monitoring systems in the Atlantic.
In planning ACCP, it was recognized that the instrumental record is too short to adequately sample decade-to-century time scales. For this reason the program contains an effort to analyze proxy data for the ocean—ice caps on land. These data can be used to constrain the models and to provide a perspective on the limited climate data available in the instrument record, which may already be contaminated by anthropogenic effects. The records from the Greenland ice cap appear to have enormous potential for the study of North Atlantic climate variability.
Plans for field activities in ACCP are guided by the results of the data analysis and modeling elements of the program. Thus, an original strategy of ACCP was to concentrate attention on the poleward transport of heat by the ocean circulation into the northern North Atlantic. In its early stages the field component of the program focused on continuation of long-term monitoring at 24°N in the Atlantic. In coordination with WOCE, a repeat section was made at 24°N in 1992 along with two shorter parallel sections in the vicinity of the western boundary. Measurements extending over nearly a decade are gradually providing details of the boundary flows near the Bahamas and in the Florida Straits. ACCP will coordinate with WOCE to continue monitoring heat transport at 24°N and to extend monitoring to higher latitudes. One of the most valuable data sources for ACCP has been the time series of hydrographic measurements taken at Bermuda and from the weather ships. While the Bermuda time series is being maintained, the weather ships no longer exist. One of the long-term goals of ACCP is to develop the instrumentation to reinstate the time series of temperature and salinity at weather ship sites in the northwestern Atlantic relying on measurements made by WOCE and other programs for the interior of the ocean.
ACCP has achieved a close working relationship with Canadian oceanographers also studying the decade-to-century climate variability in the Atlantic. Phase II of Climate Variability and Predictability, the new program of the WCRP, is focused on decade-to-century climate variability, and many of the early research accomplishments of ACCP have been incorporated in the early planning of CLIVAR. In the future CLIVAR is expected to play a major

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role in coordinating ACCP efforts with that of a larger international community interested in the role of the Atlantic in climate variability and climate change.
Box 7—Major ACCP Accomplishments
Assembly and examination of Atlantic Ocean data collected in the past.
Finding that the response to high-latitude sea-surface temperature anomalies is much more complicated than and fundamentally different from the response to tropical ocean sea-surface anomalies using atmospheric models.
Simulation of multidecadal Atlantic climate variability in the GFDL global coupled ocean-atmosphere model.
Continuation of long-term monitoring at 24°N in the Atlantic (in coordination with the WOCE program).
Establishment of a close working relationship with Canadian oceanographers studying the decade-to-century variability in the Atlantic.
Arctic Systems Science
The Arctic region has gained a prominent role in the current debate regarding global change. The Arctic comprises a mosaic of precariously balanced ecosystems that interact intimately with climate. Global climate models have shown that the largest temperature changes may occur in the Arctic. In addition the Arctic has been identified as a potentially key source of global greenhouse gases, especially methane. The recognition of the importance and sensibility of the polar regions in a changing global environment led to the creation of a new program called Arctic Systems Science (ARCSS).
The ARCSS program has two goals: (1) to understand the physical, chemical, biological, and social processes of the Arctic system that interact with the total Earth system and thus contribute to or are influenced by global change

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and (2) to improve the scientific basis for predicting environmental change on a decade-to-centuries time scale and for formulating corresponding policy options in response to the anticipated impacts of this change on humans and social systems.
Oceanographic research is a crucial component of ARCSS, although the initiative spans terrestrial, marine, and atmospheric research. The marine environment of the Arctic is an interactive system, comprising the water, ice, biota, dissolved chemicals, and sediments. Several key research areas have been identified, including the effects of energy exchange (for example, from wind or the sun) on temperature, salinity, and density distributions in the water column and carbon removal from the atmosphere and surface waters to the deep ocean and sediments via plant material. These goals are shared with WOCE and JGOFS, and in order for them to give a complete global assessment of ocean processes interrelated with climate, WOCE and JGOFS must have the knowledge of high latitudes that can be supplied through the ARCSS initiative. Because of the remoteness and inaccessibility of much of the Arctic Ocean, satellite sensors play a key role in data gathering.
ARCSS has included three components: (1) Paleoenvironmental Studies, (2) Ocean-Atmosphere-Ice Interactions (OAII), and (3) Land-Atmosphere-Ice Interactions (LAII) (Box 8). The Paleoenvironmental Studies component is, in turn, made up of two activities, the Greenland Ice Sheet Project Two (GISP2) and the Paleoclimates of Arctic Lakes and Estuaries (PALE) project.
The ARCSS Executive Committee has also identified research priorities for the future. The current categories of paleoenvironmental studies (GISP2, PALE) and studies of the contemporary environment (OAII, LAII) are expanded to include archaeology and human-environment interactions, respectively. ARCSS is funded by NSF as part of their contribution to the U.S. Global Change Research Program.

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Box 8—Major ARCSS Accomplishments
GISP2 completion of drilling for the longest environmental record ever obtained for an ice core and the longest such record that can be retrieved in the northern hemisphere. Ultimately, the core is expected to yield a 250,000-year climate history.
Precise dating and high-resolution, continuous analysis of the ice core material, yielding a detailed view of climate change well into the last glacial period. Specifically, anthropogenic effects are clearly evident during our industrial era and detailed environmental changes are visible during the last glaciation.
Establishment of research sites in poorly sampled regions and in areas particularly sensitive to rapid climate variations in the initial phase of PALE and, refinement of methods to maximize the paleoclimatic signal obtained from sediment cores.
Completion of two oceanographic cruises under OAII, resulting in a wealth of multidisciplinary data. The Northeast Water Polynya Project focused on primary productivity and biogeochemistry in polynya waters. The second study investigated the shelf waters of the Bering, Chukchi, and Beaufort seas.
OAII support for the U.S. Interagency Arctic Buoy Program and initiated modeling efforts.
LAII (initiated in late 1992) development of a detailed implementation plan for the multidisciplinary Flux Study, which will measure the rates and controls of carbon dioxide and methane fluxes along transects spanning a variety of ecosystems in northern Alaska.

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Acoustic Thermometry of Ocean Climate Project
The Acoustic Thermometry of Ocean Climate (ATOC) project is designed to characterize global climatic trends in the ocean by measuring the changes in the speed of sound along long-distance undersea paths. It rests on two principles: (i) sound speed increases with temperature, and (ii) acoustic transmissions can be monitored over gyre and basin scale ranges. This makes it possible to form synoptic horizontal temperature averages that are well suited for measuring climate change. Following a successful 1991 demonstration of the viability of acoustic travel time measurements over trans-oceanic paths (the Heard Island Experiment), ATOC was funded in early 1993 to establish a Pacific Ocean network of sound path measurements to test the feasibility of a future global network for monitoring ocean climate trends.
The advantage of using acoustical measurements is one of scale. Timing sound travel across ocean basins removes small-scale (mesoscale) variability in local temperature to reveal large spatial and temporal scale changes. ATOC has developed a plan to install mid-and eastern Pacific sound sources in the deep-ocean sound channel to establish pathways from California to New Zealand. These sources will transmit low-frequency signals to generate precise timing for sound traveling to Navy and ATOC receivers.
In the first 6 months of project activity, ATOC has established a configuration for the planned network, started construction of the sources and receivers, and developed detailed plans for their installation and operation (Box 9). The initial network will begin operational activities in early 1994 to connect North Pacific paths. Trans-equatorial paths will be established by late spring, and the network will become fully operational by late summer. To date, ATOC has met all of its planned engineering milestones and has developed contingency plans in case of changing circumstances.
Acoustic propogation studies have developed new insights into "ocean weather" effects on acoustic travel time, which will be important to the processing of ATOC data for climate trend direction. Coupled ocean climate models from the Princeton, Hamburg, and Massachusetts Institute of Technology research groups are being integrated with ATOC to provide better insights into the expected scales and distribution of global ocean change. ATOC is being funded by the Advanced Research Projects Agency (ARPA) from the Strategic

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Environmental Research and Development Projects (SERDP) through a grant to Scripps Institution of Oceanography.
Box 9—Major ATOC Accomplishments
Establishment of specific ATOC network configuration.
Development and installation of hardware including survey of existing sites and acoustic characterization of network paths.
Establishment of vertical line array designs.
Agreement on an international cooperation plan.
Scheduling of ocean ''ground truth'' measurement cruises for 1994 and 1995.
A Global Ocean-Atmosphere-Land System for Seasonal-to-Interannual Climate Prediction Program
A Global Ocean-Atmosphere-Land System (GOALS) for Seasonal-to-Interannual Climate Prediction Program was conceived as the U.S. contribution to the Climate Variability and Predictability (CLIVAR). CLIVAR is the WCRP's major new seasonal-to-interannual focused initiative. Planning for GOALS is being overseen by the National Research Council Climate Research Committee (CRC). The CRC has already completed a number of important steps, including producing a scientific background document and holding a major national scientific meeting with international representation. The CRC intends to establish a GOALS advisory panel in 1994, and GOALS will proceed with implementation plans during that year.
The ultimate scientific objectives of the GOALS program are to (1) understand global climate change variability on seasonal-to-interannual time scales; (2) to determine the extent to which this variability is predictable over time and space; and (3) to develop the observational, theoretical, and computational means to predict this variability, if feasible. A skillful forecast of average temperature and precipitation, a season to a year in advance, has

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already proven valuable in the countries in and around the tropical Pacific; an extension of predictions to the industrialized countries at higher latitudes would be of enormous economic benefit for agricultural planning, resource allocation, price support policies, and flood and drought mitigation.
The central hypothesis of GOALS is that variations in the forcing characteristics of sea-surface temperature, soil moisture, sea ice, and snow at the global boundary exert a significant influence on the seasonal-to-interannual variability of atmospheric circulation. Therefore, understanding variability and predicting climate at seasonal-to-interannual time scales requires understanding the processes that control these boundary conditions. Predicting the evolution of these boundary conditions will undoubtedly require improved models and observations.
The first phase of GOALS will augment the original prediction goals of TOGA by improving coupled models and by incorporating the data produced by the TOGA Observing System, especially the TAO Array, into predictions. Expansion into the global tropics will be based on the hypothesis that seasonal-to-interannual variability is related to variations in the locations, interactions, and effects of the major thermal sources and sinks. Expansion to higher latitudes will be guided by insights gained in studies of seasonal-to-interannual variability in the extratropical atmosphere, upper ocean, and land surfaces.
Following the successful example of the TOGA program, GOALS will be composed of four major program elements: modeling, observations, empirical studies, and process studies. The process studies will concentrate on the monsoonal forcing of the atmosphere in the eastern Pacific and Indian oceans and the transmission of these signals to higher latitudes. It is anticipated that two major ongoing TOGA activities, the TOGA Observing System and the TOGA Program on Seasonal to Interannual Prediction (T-POP) will be maintained during transition to the GOALS program. As GOALS matures, its programs can be expected to evolve and expand.
The success of GOALS will be measured in several ways: by the enhanced understanding of global climate variability and predictability on seasonal-to-interannual time scales, by the effectiveness of the observing system developed for describing and predicting the climate system, by the increased ability to model the processes involved in seasonal-to-interannual variations, and by the skill developed in predicting these variations.

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Land-Ocean Interactions in the Coastal Zone
Coastal areas of the world are zones of increasing competition between the needs of human populations and the limited resilience of natural ecosystems. Human activities exert a tremendous burden on the coastal zone on both a global scale (e.g., sea-level rise and climate change) and a local scale (e.g., land use practices and overfishing). Because existing global change research lacks strong components focused specifically on the coastal zone, the International Geosphere-Biosphere Program developed the Land-Ocean Interactions in the Coastal Zone (LOICZ) program. LOICZ defines the coastal zone as extending from the coastal plains to the edge of the continental shelf. LOICZ is based on the premise that the current use of the coastal zone will inevitably affect its use by future generations. The creation of long-term, sustainable policies for coastal management will require an understanding of the many impacts derived from changes in climate, sea-level, and land use and in the functioning of the ecosystems themselves. A LOICZ science plan has been published, and the implementation plan is scheduled for publication in late 1994.
The goals of LOICZ are: (1) to determine the fluxes of materials between land, sea, and atmosphere in the coastal zone, the capacity of coastal systems to transform and store particulate and dissolved matter, and the effects of changes in external forcing conditions on the structure and functioning of coastal ecosystems on global and regional scales; (2) to determine how changes in land use, climate, sea-level, and human activities alter the fluxes and retention of particulate matter in the coastal zone and affect coastal morphodynamics; (3) to determine how changes in coastal systems, including responses to varying terrestrial and oceanic inputs of organic matter and nutrients, will affect the global carbon cycle and the trace gas composition of the atmosphere; and (4) to assess how the responses of coastal systems to global change will affect human use and habitation of coastal areas and to develop further the scientific and socioeconomic bases for the integrated management of the coastal environment.
U.S. involvement in the LOICZ program to date has been informal. Three U.S. scientists are members of the Scientific Steering Committee, but there is no official federal agency representation or program office in the United States. Efforts continue to determine appropriate U.S. participation.